需求：

实现RSA非对称加密算法实现：public static class RSACoder {     public static final String KEY_ALGORITHM = "RSA";    private static final int KEY_SIZE = 512;    private static final String PUBLIC_KEY = "RSAPublicKey";    private static final String PRIVATE_KEY = "RSAPrivateKey";

    public static Map<String, Object> initKey() throws Exception {

        KeyPairGenerator keyPairGenerator = KeyPairGenerator                .getInstance(KEY_ALGORITHM);        keyPairGenerator.initialize(KEY_SIZE);        KeyPair keyPair = keyPairGenerator.generateKeyPair();        RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();        RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();        Map<String, Object> keyMap = new HashMap<String, Object>();        keyMap.put(PUBLIC_KEY, publicKey);        keyMap.put(PRIVATE_KEY, privateKey);        return keyMap;

    }

    public static byte[] encryptByPrivateKey(byte[] data, byte[] key)

            throws Exception {         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(key);        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);        PrivateKey privateKey = keyFactory.generatePrivate(pkcs8KeySpec);        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());        cipher.init(Cipher.ENCRYPT_MODE, privateKey);        return cipher.doFinal(data);    }

    public static byte[] encryptByPublicKey(byte[] data, byte[] key)

            throws Exception {         KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(key);        PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());        cipher.init(Cipher.ENCRYPT_MODE, pubKey);        return cipher.doFinal(data);    }

    public static byte[] decryptByPrivateKey(byte[] data, byte[] key)

            throws Exception {         PKCS8EncodedKeySpec pkcs8KeySpec = new PKCS8EncodedKeySpec(key);        KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);        PrivateKey privateKey = keyFactory.generatePrivate(pkcs8KeySpec);        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());        cipher.init(Cipher.DECRYPT_MODE, privateKey);        return cipher.doFinal(data);    }

    public static byte[] decryptByPublicKey(byte[] data, byte[] key)

            throws Exception {         KeyFactory keyFactory = KeyFactory.getInstance(KEY_ALGORITHM);        X509EncodedKeySpec x509KeySpec = new X509EncodedKeySpec(key);        PublicKey pubKey = keyFactory.generatePublic(x509KeySpec);        Cipher cipher = Cipher.getInstance(keyFactory.getAlgorithm());        cipher.init(Cipher.DECRYPT_MODE, pubKey);        return cipher.doFinal(data);    }

    public static byte[] getPrivateKey(Map<String, Object> keyMap) {

        Key key = (Key) keyMap.get(PRIVATE_KEY);        return key.getEncoded();    }

    public static byte[] getPublicKey(Map<String, Object> keyMap)

            throws Exception {         Key key = (Key) keyMap.get(PUBLIC_KEY);        return key.getEncoded();    }}

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